The confirmation of a 100,000-year warm period also raises a new question: Did global warming, and not merely “the asteroid,” make the dinosaurs go extinct? Previous studies have argued that the last non-avian dinosaurs survived roughly 30,000 years after the Chicxulub impact—which means that at least some of them endured well past the impact winter.
MacLeod isn’t yet ready to say that elevated global temperatures are what finally did the dinosaurs in. He’s currently working with another scholar, he said, to identify “specific mechanisms that were most likely responsible for killing different victims.”
“At the moment, it is safe to say the warming is another insult to those species trying to run the gauntlet between the latest Cretaceous and earliest Paleogene, including any dinosaurs that survived the immediate aftermath of the impact and subsequent impact winter,” he told me in an email.
And there may be more bad news in the study for humanity. While scientists believe that Earth’s atmosphere filled with carbon dioxide after the impact, they’re not sure how much carbon dioxide was actually released. One study finds the amount of carbon dioxide in the atmosphere increased by fivefold after the impact. “But that’s really big, it’s just one study, and geologists’ ability to estimate CO₂ levels across time is notoriously poor,” said MacLeod.
If that huge, fivefold shift is accurate, then the 5 degrees Celsius of temperature increase detected by MacLeod and his colleagues in the fish bones makes sense. The best modern climate models predict that that much warming would follow from such a gigantic release of carbon dioxide.
Yet many more studies do not argue that so much carbon dioxide was released. They say the asteroid may have only doubled carbon levels in the atmosphere. “If the increase was actually by a factor of two, or a factor of three, and if our estimate of five degrees Celsius of warming is representative of the whole globe —then the climate models are underestimating how much it will warm,” MacLeod told me.
In other words, modern climate models may be underestimating how much warming the current carbon-dioxide increase would produce. And that would be bad: It could suggest that we could see as much as twice the warming as the Intergovernmental Panel on Climate Change currently forecasts for the end of the century.
“Models are tested by their ability to reproduce what we’ve seen—and we’ve never seen anything like CO₂ levels changing at the rate they have over the last 100 years,” said MacLeod. “Or at least, we haven’t seen them since 66 million years ago.”
But that revelation lies further off. For now, the 100,000-year warmed period—produced by just the carbon emissions that occurred in the span of a human lifetime—are worrying enough. “The obvious parallel is that what we’ve done in the last century will take another 100,000 years to decay to its pre-perturbation state,” said MacLeod. “Simply stopping emissions won’t get you to where you were before, because that carbon dioxide takes a long time to cycle through our system.”